The present invention relates to a driving and positioning system consisting of a rotor equipped with permanent magnets and of a stator with at least two windings, whereby the windings are connected to an electronic voltage-supply circuit controlled by rotor-position sensors for commutating the current.
A driving and positioning system of this type is described in a 1978 brochure issued by the firm of Magnetic Technology, in which it is called a brushless DC motor. The motor is intended for various applications. It has a permanent-magnet rotor and a plated stator with a stator winding that consists of two windings. Appropriately positioned rotor-position sensors, which can be Hall sensors, determine the actual rotor position at any instant. The electronic voltage-supply circuit commutates a feed current obtained from two power amplifiers to the two coils depending on the particular rotor position detected in such a way as to produce a continuous rotation.
The effects of hysteresis in the iron circuit of the stator in such a motor and the relatively high electric time constants diminish the precision that the movement of rotation can be adjusted to and make it difficult to maintain a prescribed reference position. The motor also exhibits saturation and eddy-current phenomena in the soft iron as well as preferred mechanical rotor zero positions, leading to alternating- and direct-current losses.
Also state of the art is the brushless direct-current motor with no iron in the stator described in "A high-speed high-efficiency permanent magnetic motor-generator" by A. R. Miller, published in June 1978 by the Lincoln Laboratory, MIT, Lexington, Mass. As the rotor, equipped with a number of sector-shaped permanent magnets, rotates, it induces signal voltages in the stationary stator winding. The voltages are employed to commutate the stator current in an electronic voltage-supply circuit. This brushless motor as well makes it possible to obtain only dynamic commutation during rotation, but not to establish a desired static reference position.
German Patent Application No. 2 832 387 discloses a direct-current motor without a collector and with an axial air gap. It has axially magnetized permanent magnets mounted on a rotor plate and magnetically connected to a rotor back-connection plate. The stator consists of two star-shaped drive coils superimposed like disks and positioned on a stationary back-connection plate that can be magnetized. The rotational-position detector consists of two Hall generators. The stationary and magnetizable back-connection plate constitutes not in a non-ferrous stator, whereas there are magnetizable materials present in the alternating magnetic field.
DD Pat. No. 34 431 describes a flat and slow motor intended for directly driving flywheel masses. The stator has several flat, rather trapezoidal coils. There are no rotor-position sensors. An electronic switch can be employed as a commutator, controlling the stationary coils one after another at a prescribed rate. The current can alternatively be commutated by a collector in conjunction with slip and segment rings.